[Sema] Improving integer literal as boolean diagnostic

[LucianoPAlmeida]

Improving integer literal diagnostics to avoid test for '!= 0' instead as they don't make sense in a literal context.
Also additionally covering cases where we currently produce a Optional type 'Int?' cannot be used as a boolean; test for '!= nil' instead on contextual mismatch in situations like if 0? {} in the same way.

There is an extra case to cover on this

let variable = 0
if variable? {} // type of expression is ambiguous without more context

but that is a separate situation and is covered in another issue.

Resolves #63753

[LucianoPAlmeida]

@swift-ci Please smoke test

[hamishknight]

Thanks!

[LucianoPAlmeida]

@swift-ci Please test